1. Field of the Invention
The invention relates to a method of processing an image. The invention also relates to an image processor and to an x-ray examination apparatus.
2. Description of Related Art
The article Image filtering using multiresolution representation in the IEEE Transactions of Pattern Analysis and Machine Intelligence, 13(1991)426-440, by S. Ranganath, discloses a method for processing an image, wherein the image is decomposed into detail images at successive resolution levels, and the detail images are filtered so as to generate filtered detail images. The processed image is reconstructed from the filtered detail images.
The cited reference discloses image filtering using multiresolution representation. Image filtering is implemented as the convolution of the image and a two-dimensional mask. Preferably, a pyramid structure is applied for the multiresolution representation. In the cited reference the detail images of the multiresolution representation implemented by the pyramid structure are named `coded images`. The cited reference mentions that the `coded images` are filtered. The known method aims at achieving a good compromise between noise removal and loss of resolution. It has been found that the known method is not satisfactory with respect to reducing noise while retaining edges in the image. In particular, the known method is not suitable for producing a processed medical image having a high diagnostic quality, i.e. an image in which small details having low contrast are displayed so as to properly visible.